AES E-Library

AES E-Library

Measurement of Loudspeakers with a Laser Doppler Vibrometer and the Exponential Sine Sweep Excitation Technique

In order to explore the vibrations of a loudspeaker cone, this research measures the axial acceleration of hundreds of points on the cone surface employing a Laser Doppler Vibrometer when excited by an exponential swept sine signal. The recorded signal was then transformed into an impulse response by convolution with the matched inverse sweep signal. From the knowledge of the acceleration at each point of the radiating surface, the free field sound pressure on axis at 1-m distance was computed. This research obtained results comparable to Finite Element Method simulations based only on the linear mechanical behavior of the loudspeaker cone without any acoustic interference. Moreover, by comparing the laser measurements of many samples, the researchers evaluated how the influence of known variations in the loudspeaker components or production process influenced the final performances of the device. Postprocessing of experimental results was performed using Matlab scripts, which also computed the deflection shapes of the loudspeaker cone.